Superabsorbent polymers are polymeric materials capable of absorbing many times their own weight of water and other liquids. Commercially, these polymeric materials are used as additives to increase the absorbency of disposable articles such as diapers, adult incontinence pads, feminine hygiene pads, tampons and the like.
Superabsorbent polymers are commonly used as powders or granules. If not immobilized, the powdered material may bunch up or agglomerate, resulting in uneven absorptive capacity or discomfort, or may become air-borne, resulting in health risks due to swelling of particulate within human air passages.
A variety of methods have been suggested to provide immobilization of superabsorbent polymer (SAP) particulate. PCT application WO 90/11181 describes a fiber product in which discontinuous fibers are coated using a mist of a liquid binder material, and superabsorbent particulate is applied to the binder-wetted fibers. Particulate adhesion is provided by drying or heating. Also described is forming a mixture of SAP particulate in a melt. European Patent Application 425,269 describes use of such a melt for melt-spinning fiber which may be cellulose acetate fiber. U.S. patent application Ser. No. 07/805,538, filed on Dec. 11, 1991, describes forming a suspension of SAP particles in a solvated matrix material which may be a cellulose ester, for extruding or casting.
In addition, U.S. Pat. Nos. 3,966,679 to Gross, 4,444,830 to Erickson, 4,600,462 to Watt and 4,468,428 to Early et al illustrate absorbent materials including SAP as an additive. Generally speaking, in this type of prior work, a binder is also used, or SAP is formed in situ on a substrate. In the Watt patent, an air laid, cellulosic fiber web is treated with a hydrophobic binder and a hydrophile. Erickson and Gross describe coating an aqueous polymer solution including a cross-linking agent, onto a substrate to form a coating of SAP. Erickson coats a fibrous material which is thereafter mechanically worked to form a discontinuous fiber matrix. Erickson suggests starch/graft copolymers may also be used. The coating of Gross may be continuous or discontinuous.
Continuous filament, cellulose ester tow having crimped filaments, is commercially available from Hoechst Celanese Corporation of Charlotte, N.C. For cigarette filter applications, the tow is opened and thereafter treated with triacetin or a similar agent to build hardness, and the treated tow is formed into a filter.
Manufacturers of absorbent articles are striving to make ever thinner absorbent products while maximizing fluid absorption. In the past, these efforts have been hampered by: pad having poor strength in the machine direction that limits production rates and in-use performance; and lack of immobilization of the superabsorbent material. The prior art discussed above is directed primarily to the solution of the latter problem.
Accordingly, despite advances in absorbent products, an improved absorbent article including superabsorbent particulate is needed. Beneficially, the superabsorbent particulate would be immobilized in a high integrity web. Advantageously, immobilization would be achieved without deleteriously affecting absorptive capacity. Accordingly, there is a need for an improved process for providing superabsorbent fiber loaded with immobilized superabsorbent particulate, and yet that maintains absorptive capacity.